U.S. Pat. No. 4,550,148, granted Oct. 29, 1985 to Droescher, discloses molding compositions of polyalkylene terephthalate, isocyanate with functionality of 3-7, and optionally, other polymers conventional in polyester technology, such as polyamides, polyetherester amides, polyether esters, and functionalized ethylene/propylene/diene/copolymer (EPDM). The functionality of the isocyanate disclosed in this reference is beyond the literal scope of the isocyanate claimed in the present invention.
U.S. Pat. No. 4,409,167, granted Oct. 11, 1983 to Kolouch et al., discloses a process for extruding polymeric blends consisting of poly(ethylene terephthalate) resin with an incompatible polymer that is made compatible to the poly(ethylene terephthalate) resin through the use of a compatibilizing agent, such as carboxyl- or ester-containing polymers. Organic diisocyanates are used only to increase the melt viscosity of the composition. The present invention eliminates the requirement that a compatibilizing polymer be used when an incompatible polymer is blended with poly(ethylene terephthalate).
U.S. Defensive Publication T-908,011, published Mar. 27, 1973 by Witsiepe, discloses a modified polyester composition prepared by mixing copolyester polymer with a polyisocyanate. The polyisocyanate is used to increase the number average molecular weight of the polyester composition. There is no mention in the reference of a blend of incompatible polymers.
U.S. Pat. No. 3,697,624, granted Oct. 10, 1974 to Braunstein, discloses a modified oxymethylene polymer prepared by the coupling reaction of an oxymethylene polymer (acetal polymer) and polybutylene terephthalate with an isocyanate. This is a blend of two hard polymers (i.e., polymers having flexural modulus greater than 150 kpsi).
While the above references all disclose blends consisting at least of a polyalkylene terephthalate and an isocyanate, none disclose the particular claimed blends of the present invention nor do any recognize the improved results obtained with such blends.